A phased array system includes N identical radiators supported as an array. Separate phase shifter means is connected in series with any number of the radiators and N identical microwave power amplifier tubes feed the respective radiator and phase shifter combinations. The microwave power tubes provide in-phase identical outputs. A tube may arc or it may fall entirely. It has been conventional practice to include protective circuitry in the transmitter for responding to arcing to terminate power to the tube. Whether there is arcing or the tube falls, the tube output ceases and the array is effectively inoperative. The most primitive method of correcting the condition has been to shut down to replace the defective tube. This method was improved by running an additional tube into a dummy load as a standby and upon non-operation of one of the tubes feeding one of the radiators, operating a valve-type waveguide switching device to switch in the standby tube. This method was automated by monitoring microwave power output of each feed tube and including relay-controlled solenoid-operated valve-type waveguide switching devices between the tubes and the radiators so that if any of the tubes failed, the switching devices rearranged the relationship of tubes and radiators fed thereby, so that every radiator was fed by a tube after switching. A three-port circulator coupled the standby tube alternatively to a dummy load or to one of the solenoid-operated valve-type microwave switches. Besides being cumbersome, this system is too slow, having 0.1 second to 0.5 second response time. A number of pulse periods are lost in that time. For radars having missile sensing functions, loss of several pulse periods at a critical juncture requires correction.